The present invention relates to the general field of using a method of molding by injecting a liquid resin, known as resin transfer molding (RTM), for making a composite material part having a closed portion in the form of a box.
An example application lies with fabricating fan blade platforms out of composite material for an aviation turbine engine fan.
The fan blade platforms of a turbine engine, in particular of a turbojet, are arranged between the fan blades so as to extend the inlet cone of the fan. They serve in particular to define the inside of the annular air inlet passage into the fan, which passage is defined on the outside by a casing.
Document WO 2013/160584 discloses a method of making a fiber blank that is woven as a single piece by three-dimensional (3D) weaving for the purpose of fabricating a fan blade platform having a closed box under the base of the platform that serves to define the inside of the annular air inlet passage into the fan. The presence of a closed box thus serves to reinforce the mechanical strength of the blade platform.
Once such a fiber blank has been made, it is shaped so as to obtain a fiber preform. The fiber preform is then positioned in the cavity of an injection mold with a core (or mandrel) being placed inside the closed box of the preform. The cavity of the injection mold is then filled with epoxy resin in order to impregnate the preform. The resin is polymerized, thereby forming a matrix in which the preform is embedded, and then at the end of resin injection, the temperature of the mold is lowered in order to unmold the part.
In general manner, the step of unmolding the part is important and difficult to perform since the design of the injection tooling needs to include provision for means that facilitate unmolding the part and that are adapted to its shape. In the application to fabricating a fan blade platform, the main difficulty in unmolding the resulting part lies in extracting the core that is placed inside the box of the preform. The size of the opening section of the box through which the core is extracted is smaller than the maximum section of the core positioned inside the box. Given this difference in section size, it is not possible to extract the core from the box of the part.